1. Field of the Invention
The invention relates to novel aromatic acids, especially compounds of formula ##STR2## wherein R.sub.1 is lower alkyl, R.sub.2 is lower alkyl, R.sub.3 is hydrogen, carboxy or sulfo, R.sub.4 is carboxy or sulfo, G is an unsubstituted or substituted 1,4-phenylene group or an unsubstituted or substituted 1,4-naphthylene group, and wherein either R.sub.5 and R.sub.6 together are an additional bond and L is an oxygen or sulfur atom or wherein R.sub.5 is hydrogen, R.sub.6 is halomethyl and L is an oxygen atom, and salts thereof, to the use of compounds I and their salts, to a process for the preparation of compounds I and their salts, to starting materials used in that preparation process, and salts thereof, to a process for the preparation of those starting materials and their salts, to a device in which the compounds I and their salts are used, and to a process in which that device is used.
Suitable unsubstituted or substituted 1,4-phenylene groups are, for example, unsubstituted or carboxy- and/or sulfo-substituted 1,4-phenylene groups, the substituted 1,4-phenylene groups having from 1 up to and including 4, especially 1 or 2, of the mentioned substituents. If the substituted 1,4-phenylene groups contain more than one substituent, then some or all of those substituents may be identical. Examples that may be mentioned are the 2-sulfo-, 2,3-, 2,5- and 3,5-disulfo-, 2,3,5-trisulfo- and 2,3,5,6-tetrasulfo-1,4-phenylene group, the 2-carboxy-, 2,3-, 2,5- and 3,5-dicarboxy-, 2,3,5-tricarboxy- and 2,3,5,6-tetracarboxy-1,4-phenylene group, the 2-carboxy-3-sulfo-, 2-carboxy-5-sulfo-, 3-carboxy-5-sulfo-, 2,3-dicarboxy-5-sulfo-, 3,5-dicarboxy-2-sulfo-, 5-carboxy-2,3-disulfo- and 2-carboxy-3,5-disulfo-1,4-phenylene group and especially the 1,4-phenylene group.
Suitable unsubstituted or substituted 1,4-naphthylene groups are, for example, unsubstituted or carboxy- and/or sulfo-substituted 1,4-naphthylene groups, the substituted 1,4-naphthylene groups containing from 1 up to and including 6, especially from 1 up to and including 3, of the mentioned substituents. If the substituted 1,4-naphthylene groups contain more than one substituent, then some or all of those substituents may be identical. Examples that may be mentioned are the 2-, 5- and 6-sulfo-, 2,3-, 5,6-, 6,7- and 2,6-disulfo-, 2,3,5- and 2,3,6-trisulfo- and 2,3,5,7- and 2,3,6,7-tetrasulfo-1,4-naphthylene group, the 2-, 5- and 6-carboxy-, 2,3-, 5,6-, 6,7- and 2,6-dicarboxy-, 2,3,5- and 2,3,6-tricarboxy- and 2,3,5,7- and 2,3,6,7-tetracarboxy-1,4-naphthylene group, the 2-carboxy-3-sulfo-, 2-carboxy-5-sulfo-, 3-carboxy-6-sulfo-, 5-carboxy-7-sulfo-, 2,3-dicarboxy-5-sulfo-, 3,5-dicarboxy-2-sulfo-, 6,7-dicarboxy-2-sulfo-, 3-carboxy-6,7-disulfo-, 5-carboxy-2,3-disulfo-and 2-carboxy-3,5-disulfo-1,4-naphthylene group and especially the 1,4-naphthylene group.
The invention relates, for example, to compounds I wherein R.sub.1 is lower alkyl, R.sub.2 is lower alkyl, R.sub.3 is hydrogen, carboxy or sulfo, R.sub.4 is carboxy or sulfo, G is an unsubstituted or substituted 1,4-phenylene group or an unsubstituted or substituted 1,4-naphthylene group, R.sub.5 and R.sub.6 together are an additional bond and L is an oxygen or sulfur atom, and salts thereof.
Some of the compounds I can be in the form of stereoisomers. For example, if the compounds I contain at least one chiral carbon atom (C atom) (for example a C atom of a corresponding radical R.sub.1), they can be, for example, in the form of pure enantiomers or mixtures of enantiomers, such as racemates, and if there is at least one further chiral centre present (for example a C atom of a corresponding radical R.sub.2), they may also be in the form of diastereoisomers, mixtures of diastereoisomers or mixtures of racemates.
Salts of compounds I are especially salts with bases, preferably pharmaceutically acceptable salts with bases, for example alkali metal salts or alkaline earth metal salts, for example sodium, potassium or magnesium salts, transition metal salts, such as zinc or copper salts, or salts with ammonia or organic amines, such as cyclic amines, such as mono-, di- or tri-lower alkylamines, such as hydroxy-lower alkylamines, for example mono-, di- or tri-hydroxy-lower alkylamines, hydroxy-lower alkyl-lower alkylamines or polyhydroxy-lower alkylamines. Cyclic amines are, for example, morpholine, thiomorpholine, piperidine or pyrrolidine. Suitable mono-lower alkylamines are, for example, ethylamine or tert.-butylamine; suitable di-lower alkylamines are, for example, diethylamine or diisopropyl-amine; and suitable tri-lower alkylamines are, for example, trimethylamine or triethylamine. Suitable hydroxy-lower alkylamines are, for example, mono-, di- or tri-ethanolamine, and hydroxy-lower alkyl-lower alkylamines are, for example, N,N-dimethylamino- or N,N-diethylamino-ethanol, whilst a suitable polyhydroxy-lower alkylamine is, for example, glucosamine. The compounds I can also form acid addition salts, preferably pharmaceutically acceptable acid addition salts, for example with strong inorganic acids, such as mineral acids, for example sulfuric acid, a phosphoric acid or a hydrohalic acid, with strong organic carboxylic acids, such as lower alkanecarboxylic acids, for example acetic acid, saturated or unsaturated dicarboxylic acids, for example malonic, maleic or fumaric acid, or hydroxycarboxylic acids, for example tartaric or citric acid, or with sulfonic acids, such as lower alkanesulfonic acids or unsubstituted or substituted benzenesulfonic acids, for example methane- or p-toluene-sulfonic acid. The compounds I can also form inner salts.
Also included are salts of compounds I that are less suitable for pharmaceutical uses. These may be used, for example, for the isolation or purification of free compounds I according to the invention and their pharmaceutically acceptable salts.
Hereinbefore and hereinafter, unless defined otherwise, radicals or compounds designated "lower" are to be understood as being especially those radicals or compounds containing up to and including 7, especially up to and including 4, carbon atoms.
Lower alkyl is, for example, C.sub.1 -C.sub.4 alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec.-butyl or tert.-butyl, and also includes C.sub.5 -C.sub.7 alkyl radicals, that is to say pentyl, hexyl and heptyl radicals.
2. Description of the Related Art
Halomethyl is fluoro-, chloro- or bromo-methyl, but especially iodomethyl.
The compounds I and their salts have valuable properties. For example, they can be used as adjuncts in the investigation of proteins, for example as reagents for the chemical modification of proteins. Hereinbefore and hereinafter the term "protein" is to be understood as including both peptides having a relative molecular weight of 10 000 or more atomic mass units, which are generally termed proteins, and peptides having a relative molecular weight of less than 10 000 atomic mass units, which are generally termed polypeptides, a lower limit of from approximately 1000 to approximately 2000 atomic mass units applying to the relative molecular weight of the polypeptides. Examples taken from the numerous applications in which the chemical modification of proteins can play a part are the structural analysis and the coloration of proteins.
It is known that the modification of a single amino acid building block or of a small number thereof can substantially alter the spatial structure of a protein and therefore also its function, for example its biological activity. This opens up the possibility of using the specific chemical modification of amino acid building blocks as a widely applicable method of determining the contribution made by these building blocks to the spatial structure of a protein. The problem arises here of relating any alteration in the spatial protein structure occurring as a result of a certain chemical modification of amino acid building blocks to the nature and extent of that chemical modification. For this purpose the structure of a corresponding chemically modified protein must be determined and compared with the structure present before the chemical modification was carried out. One of the aims of this kind of structural analysis is to determine in what way the protein primary structure has changed during the chemical modification, that is to say which amino acid building blocks have been chemically modified. In primary structure analyses of this kind, the procedure is often as follows: a chemically modified protein M.sub.a, obtained after chemical modification of a corresponding unmodified protein N.sub.a, and the unmodified protein N.sub.a are, optionally after having carried out a denaturation step which may be necessary, each treated with the same protease, the two peptide mixtures M.sub.a.sup.1 and N.sub.a.sup.1 so obtained are each subjected to high-performance liquid chromatography (HPLC) and the peak patterns in the two resulting chromatograms M.sub.a.sup.2 and N.sub.a.sup.2 are compared with one another. The detection systems used for recording these chromatograms are usually detection systems which evaluate the light absorption behaviour of the peptides. The peak pattern in chromatogram M.sub.a.sup.2 generally differs from the peak pattern in chromatogram N.sub.a.sup.2 at those places at which peptides M.sub.a.sup.3, which contain at least one chemically modified amino acid building block, are detected, since the peptides M.sub.a.sup.3 generally exhibit a light absorption behaviour different from that of the corresponding unmodified peptides N.sub.a.sup.3. The peptides M.sub.a.sup.3 are separated off and subjected to further primary structure analysis, for example to amino acid sequence analysis. Ideally, each chemically modified amino acid building block can be identified and characterised in this manner.
In many cases, however, the usefulness of the above-described procedure leaves something to be desired. For example, when the protein to be investigated has a relatively high relative molecular weight, there are normally so many different peptides present in the corresponding peptide mixture after the protease treatment that HPLC is unable to effect sufficient separation of the peptide mixture. Furthermore, the chemical modification itself is often too complex; it often proceeds in a non-specific manner and therefore affects a large number of structurally different amino acid building blocks or even all the amino acid building blocks in the protein under investigation; advantageously, however, it should be possible to carry out the chemical modification as specifically as possible, that is to say specifically directed only at a class of amino acid building blocks that is defined as accurately as possible and advantageously that is narrowly defined in terms of nature and number.
It is therefore desirable and of great practical interest to optimise the procedure described above by overcoming the disadvantages indicated. The compounds I disclosed within the framework of the present invention and their salts make such an optimisation possible. This optimisation is explained in detail below with reference to compounds I in which R.sub.1, R.sub.2, R.sub.3, R.sub.4 and G are as defined above, R.sub.5 and R.sub.6 together are an additional bond and L is an oxygen or sulfur atom, and salts thereof. These compounds are designated compounds IA below.